Whilst developing my unattended Windows XP build, I came across a number of devices that were not automatically detected by Windows.
Sometimes, right-clicking the unknown device in Device Manager and selecting the Update driver... option allowed Windows Update to connect to the Internet and locate updated drivers (which in turn identified the device and allowed me to download and integrate the OEM drivers into the Windows XP installation source).
On other occasions it was not so simple, and I needed to do some research to identify the device using the PCI device instance ID (found on the details page of the device properties).
A couple of years back I was introduced to Craig Hart's PCI and AGP bus sniffer. I could just run the utility, but in this case I chose to search its companion file (pcidevs.txt) for the vendor and device PCI IDs. Using this technique, I was able to identify my unknown device as the Broadcom (vendor 14E4) BCM4306 802.11g Wireless NIC (device 4320), which is also known as a Dell Wireless 1350. Once I had that information, all that was required was to download the drivers for integration.